Ethical dilemmas: is walking more polluting than driving?
Las Vegas, Nevada - The rule of our journey around America is straightforward: where there is a choice we take the low-carbon option. It sounds simple but making the right choice can be difficult.
Here is a case in point. On Tuesday I met my first bona fide billionaire, the oil-man turned wind energy tycoon, T Boone Pickens.
I interviewed him in his Dallas office and, as we chatted afterwards, I mentioned we were heading off to Las Vegas. Boone, being a true Oklahoma gentleman, promptly offered us a lift... on his private plane!
My other attempt at hitch-hiking, back in Detroit, ended with me being stopped by the police. Boone was much more accommodating. He said he was going to Phoenix early Friday morning and would be happy to get his plane to drop us in Vegas.
What a dilemma! Two hours relaxing in the soft leather seats of a billionaire's private jet or 20 hours behind the wheel of a hire car (there is no connecting train and at 28 hours, we judged the Greyhound just too time consuming).
It should be a straightforward calculation: Boone was already going to Phoenix so it is the marginal increase in jet fuel against the emissions of the petrol consumed by a car making the 1,200 mile journey by road.
It is a much more glamorous version of the sort "ethical" dilemma I became far too familiar with during the year my family and I lived as Ethical Man. What I learned then is that these calculations are rarely as simple as they seem.
I stumbled across a great example of this last year. In the spirit of recycling I have lifted it straight from a blog by a guy called Brad Templeton.
Brad explains that the average person uses about 100 calories per mile walking at 3 mph - 300 calories per hour. By comparison sitting burns 80 calories an hour. In other words, walking three miles takes an extra 220 calories.
Now, a (US) gallon of gasoline has about 31,500 calories so the conclusion might be that a human walking gets around 400 mpg. But, as Brad points out, that ignores the fossil fuels that go into producing the food we eat.
Brad claims US agriculture uses about 400 gasoline-gallon equivalents per American per year (if anyone can source this figure I would be very grateful). So that is 1.1 gallons a day to produce the 2700 calories that form the average American's diet or 10 calories of fossil fuel for each calorie of food consumed. That is right: 10 fuel calories for each food calorie! It is a shocking statistic isn't it?
You will have guessed where this is going: walking 3 miles uses 220 extra calories over sitting, but sucks up 2,200 calories of fossil fuel. This means you get just 42 mpg as you stroll. Some small cars are more efficient.
And, if you eat a lot of burgers, the figures are even worse. Your fuel consumption rises dramatically because 40 calories of fuel energy are used per calorie of beef. If you only ate beef you would not only be very unhealthy, you would get just 10 mpg as you walked, worse than a Humvee!
On this basis the correct choice would be for the Ethical Man team to drive rather than walk whenever possible (sharing a vehicle dramatically improves fuel efficiency).
Nonsense, of course, but Brad's calculations make an important point - and not just that modern agribusiness uses an extraordinary amount of energy. You may quibble with some of his figures but his example shows just how complex it is can be to work out the carbon cost of different activities.
Which is why the arguments for cap-and-trade can be compelling. If we have to pay to emit carbon dioxide it will be much easier to make the environmental choice because the low carbon option will become the cheaper option.
At the moment prices reflect the scarcity of fossil fuels, which is why I was able to afford to buy a return ticket from Los Angeles to London this weekend (it cost just £400, plus £40 for a carbon offset). That's right, I have flown home for the weekend!
I have to host a charity dinner which was arranged before we planned our American odyssey. (It is for my wife's favourite charity, Friends of Colombia for Social Aid, if you are interested.) I will also get to spend a few hours with my lovely family who I have been missing terribly over the last three weeks.
But the question I opened this blog with was about a billionaire's private jet, not me missing my family.
So did we accept Boone's kind offer? We did not, but not because of concerns about the carbon cost. I mean, how many times have you been offered a ride to Vegas in a billionaire's private jet?
The reason did not accept was because Boone was flying on Friday and we had arranged to meet Las Vegas' only pig farmer and one of Nevada's leading food recyclers on Thursday morning.
The farmer, Bob Combs, is a perfect example of conservation in action. He collects the food waste from the ludicrously extravagant buffets laid on by Las Vegas hotels and then cooks it up and feeds it to his pigs. His hogs recycle some of those food calories that so concern Brad Templeton.
Judge for yourself whether we were right to forgo the jet and meet Bob. And, of course, feel free to comment below. You can complain about my decision to take a break from this trip and catch a plane home or maybe even sympathise with me. Did I make the right choice?